Reflecting electric lamp



c. BIRDSEYE ET AL 2,121,314

REFLECTING ELECTRIC LAMP June 21,- 1935.

Filed Dec. 19, 1935 5 Sheets-Sheet 1 c. BIRDSEYE E'r- AL REFLECTING ELECTRIC LAMP Filed Dec. 19, 1935 June 21,1933.

3 Sheets-Sheet 3 Patented June 21, 1938 UNITED STATES PATENT OFFICE REFLECTING ELECTRIC m ration of Delaware Application December .19, 1935, Serial No. 55,208

Claims.

This invention concerns. improvements in the design of reflecting electric lamps and particularly lamps adapted for indirect or coive lighting, that is, lamps adapted to be placed in a cove 5 or channel near the junction of the wall and ceiling of a room, concealed from the direct view and so designed and placed that their radiation is directed generally toward predetermined portions of the ceiling of said room, whereby the 1 illumination of objects below is obtained by diffuse reflection from the ceiling.

As is well known, indirect or cove lighting, while highly desirable from many ,viewpoints is in general far less eflicient than direct lighting. It is therefore particularly important in this field that the lamps themselves be of the highest possible efiiciency in addition to having the other qualifications which may be more directly related .to the problem. A

When standard lamps are used in indirect lighting installations, and placed horizontally in the cove, adjacent an external reflector, asymmetrical light patterns on the ceiling result from the lack of symmetry of the individual bulbs. Such asymmetrical light patterns are highly objectionable from the decorative and efficiency standpoints. If the bulbs are placed vertically in order to avoid. this asymmetry of lightpattern, an excessively large reflector and an unduly large cove become necessary thus entailing considerable expense, and possibly conflicting with the architectural design of the room. The external reflector required, whether the bulbs be placed horizontally or at some other angle, is in addition an inefioient reflector. I

It is an object of .this invention to provide a lamp which is peculiarly adapted to indirect or cove lighting installations in that it results in a.

marked improvement in lighting eificiency when so used. 9

Another object of this invention is to provide a lamp which ispeculiarly adapted to indirect or cove lighting installations insofar as it produces a symmetrical light pattern on the ceiling although placed with its axis horizontal.

It is a further object of the invention to provide a lamp peculiarly adapted to indirect or cove lighting installations in the sense that it is a self contained unit, radiator and reflector comprising 50 a single compact structure, and requiring a cove of minimum space requirements.

The preferred form of lamp in accordance with the invention comprises a bulb having a reflecting coating over one-half or approximately onehalf its surface, the coating being bounded by a plane in which lies the axis of the bulb, and the bulb itself being symmetrical not only about its own axis but also, with the exception of the neck portion thereof, about an axis perpendicular to the axis of the bulb. In addition we provide our preferred bulb with a neck reflector which, contrary to the teachings of the prior art, is not mounted with its axis coincident with the axis of the bulb, but at a considerable angle therewith, so that radiation from the filament which strikes this neck reflector will not only be prevented from being absorbed in the mount but will also be immediately reflected out through the transparent wall of the bulb. This construction thus in two senses, first by'eliminating absorption, and second by eliminating multiple reflection, improves efllciency. The neck refiector is so formed and placed that its reflecting surface is a substantial continuation of the symmetrical reflecting surface of the bulb itself.

This results in a symmetrical radiation pattern on the ceiling when the bulb is in use.

In another form of the invention, useful where decorative features are not of paramount importance, we employ a bulb of standard outward form, which results in considerable economy. In this case, we prefer to employ a neck reflector, either dished or plane, and carefully mounted at such an angle that light rays from the filament impinging thereon will be immediately reflected outward of the bulb. Elimination of multiple reflection and consequent improvement of efficiency is also assisted in some measure byplacing the filament not directly at the center of the bulb as in the common practice, but somewhat offset toward the reflecting side thereof. In the case of a bulb of standard form, which is not symmetrical about an axis perpendicular to that of the bulb, some improvement in the symmetry of the illumination pattern may be achieved: by moving the filament slightly'in the direction of the neck from its usual position. The amount of this preferred displacement is ofthe order of one-quarter inch for a standard 3(l0-watt'bulb. When; as in any of the subordinate forms of our invention, the filament is positioned wholly within the reflecting area, and thus below the main axis of the lamp, we have found it desirable to bring the lead-in wires and any other filament supports, insulated if necessary, through the sloping oval reflector at the edge of the reflector, rather than through its center, thus leaving the main part of this reflector a smoothunmarred surface. Thiscan also be accomplished by passing them through small holes near the edge of the reflector or through small slits at the edgeond, the improvement in efllciency of illumination. This invention covers means for achieving these results in combination, as in the preferred form, or separately. In case only one of the results is desired, for example, the improved efllciency, the invention again covers various means, as briefly outlined above and as explained in greater detail in connection with the diagrams the generic feature being the elimination 10 as far as possible of successive reflections within the bulb.

These and other features of the invention will be best understood and appreciated from the following description of several preferred embodi- 15 ments thereof selected for purposes of illustration and shown in the accompanying drawings in which,- Fig. l is a view in vertical cross section, partly in elevation of a lamp in horizontal pomtion havan ing a reflecting coating applied to its lower half, together with a polar intensity diagram of the light emitted thereby.

Fig. 2 is a similar view of a lamp equipped with a neck reflector and the corresponding light diagram Fig. 3 is a similar view of a-lamp having a modifled shape and the corresponding light diagram- Fig. 4 is a similar view of a lamp having its 80 shape still further modified and a corresponding li ht dia ram. and

Fig.5isasimilarviewofalamp of the general charactershown in Fig. 2 but having as an additional feature an offset filament, together 85' with the corresponding light diagram.

In Fig. l is shown a reflecting electric lamp having a bulb of standard shape with a silvered reflecting surface applied to the lower half of the bulb and limited by a horizontal plane passing 40 through the main axis of the lamp. The bulb is formed with the conventional cylindrical neck portion and adjacent conical portion and a spherical or bowl portion and the filament is located substantially at the center of curvature I of the bowl portion of the bulb. The silvered coating is appliedto the lower half of the conical and bowl portions of the bulb in such'a manner as to reflect light from the light source as indicated in the drawings by the various arrows so shown. The incident rays and the reflected rays will coincide over the spherical part of the reflecting surfaces, in the case of a point source of light located at the center of the spherical part of the bulb, although of course the angles of in- 66. cidence and reflection will not be exactly 90, and will not exactly coincide, when the light rays are emitted from those parts of the filement not at the center of the spherical part of the bulb.

.0 The continuous heavy line starting from the fllament center, 0, and marked A, B, and C and then returning back to 0, represent the polar intensity diagram for such a lamp, assuming spherical emission from a point source at the ll center of the fllament, and with 80% reflection efllciency. The case where the fllament is not a point but an ordinary extended fllament, would bemuch like this diagram, except that the edges wouldnotbesharplydeflned. Inordertomake 70 simpler, in each of the several draw-' ings where thesediagrams are shown, the above assumptions have been uniformly applied.

A straight line drawn'from 0 to any point on thiscm've,A,B,Cisproportionaltothe light tlintensityinthedirectionofthestraightline,

The diagram and the representation of the lamp axis as shown are assumed to lie in' the plane of the paper on which they are drawn, the line which bounds the silvered surface of the bulb lying in a plane perpendicular to the plane of the 5 paper. Since this bulb, and therefore the reflecting surface, is symmetrical about the axis of the lamp, any polar intensity diagram on any plane through the lamp axis will have this same shape. It will be noted that the part of the diagram marked C, represents the intensity from the direct light only, since no reflected light is sent in the direction of this part of the curve. This intensity of direct light is equal in all directions and in all planes the polar intensity diagram for this direct light only would be the dotted circle continuing from the point 8 throughC to the point 1. The part marked A represents the sum of the intensities of the direct light and of the light reflected from the spherical part of the reflecting surface. The spherical reflecting surface reflects light of uniform intensity from the line O-N to the line O4, and the polar intensity diagram for this sum would be a -circle- 26 shown partly dottedfrom the point 9, through A to the axis N-N'. 'However, that part of both the direct light and the reflected light from the spherical part of the reflecting surface, falling betweenthe cut-off line O-2 and the axis N-N 30 is largely lost in the neck section, as is the direct light between O--I and the axis N-N'.

The conical part of the reflecting surface reflects light between the limiting raysindicated .asO-4andO5,andthisefl'ectistransferred as to the polar diagram between the radii O4 and 0-3, the latter being parallel to the limiting ray O5. The part, B, of the polar intensity diagram therefore represents the sum of the direct light, the light reflected from the spherical part 40 of the reflecting surface, and the light reflected from the conical part of the reflecting surface. In Fig. 2 is shown this same lamp of standard shape with a sloping dished oval shaped reflector 20 podtioned in the stem, and serving approximately as a continuation of the conical part of the reflecting surface. The polar intensity dis gram is derived in the same manner as explained for Fig. 1. The light which would otherwise be lost in the neck of the lamp is here reflected out so of the bulb by means of the sloping reflector. The limiting ray, marked 5, in this area, which determines the location of the parallel radius 0-4 in the polar intensity diagram, shows the improvement in eifective reflection, and may be noted by the cross-hatched area between the part of the curve marked B, and the dotted circle 2-A9. The cut-off angle, made by the line 0-2 andtheaxisN-N' hasherealsobeenimproved somewhat, resulting in a further utilisa- 00 tion of light.

Inl'ig.3isshownabulbhavingacylindrical neck, and an adjacent conical section, but with the ordinary spherical portion elongated in shape, .sothat thebulb endsinabhmt tip. At thevery 05 tip, such a bulb, and therefore the reflecting surface upon it, would of course be P p dicular totheaxisNN', andtheraystriklngthe re-- flectingsurface atthispointwouldbereflected back to the sloping reflector. However the amount of light involved and so reflected twice is of little practical importance, and to avoid such ne li ible loss, it would be advisable to limit thereflecting'surfaeebyaplane just below ratberthanthrwghtheansN-N'. 'meprac- 7i ticallimiting ray reflected from this part of the reflecting surface is that marked 6, and it is reflected directly out of the bulb, as are all other reflected rays from the reflecting surface of this .bulb. The polar intensity diagram has been developed as in Fig. 1. The direct light accounts for the circle-part dotted-2-A-C-8, and the reflected light from the, conical surface plus the direct light'in this direction is shown by the dotted sloping curve D. The irregular curve marked B indicates the sum of the intensities of the direct light, ahd the reflected light from both the conical and the elongated bulbous portion of the reflecting surface.

Fig. 4 shows a bulb of spherical shape that is not only symmetrical about its main axis N- -'-N,

but which-except for the neck areafi-is symmetrical with respect to the plane perpendicular to the main axis, andshown in thedrawings by thetrace M-M'. A sloping dished reflector 2| is positioned in the neck and approximates a continuation of the reflecting surface of the bulb, and so completes the symmetrical relationship with respect to the plane, marked M--M'. The sloping reflector 2| extends above the main axis NN, in order to prevent light loss in the neck; and the little bump on the polar intensity diagram, between the radii O--9 and -4, is due to light from the upper part of this sloping reflector. Actually this part of the sloping reflector above the axis NN' reflects the light that would normally be emitted as direct light between the radius 0-2 and the axis, N-N', and so lost in the neck, and reflects it as shown in the diagram, between 0-1 and 0-9, thus causing the bump.

It should be noted thatthe polar intensity diagram is symmetrical in this case, except for the small bump, discussed above. A symmetrical "diagram will result from a bulb symmetrical about its main axis used in this manner, with half its surface acting as a reflector in the manner shown, provided the bulb is also sym-' metrical with respect to a plane perpendicular to the main axis and passing through the largest diameter of the bulb, almost without regard to theexact shape of the trace made by a plane passing through the reflecting surface and through the main axis of the bulb. Thus we do not desire to limit our invention as embodied in this type of lamp to the exact shape shown in Fig. 4, but would include within its scope all x symmetrical bulbs having any reasonable shape for the trace of the surface of the general character shown as D and E in Fig. 4.

In Fig. is shown a lamp in the structure of which is included a standard bulb having a'silvered reflecting coating applied to its lower half and bounded by a horizontal plane through the major axis of the bulb. The fllament 23 is located below the main axis of the lamp so that it is completely hooded by the reflecting surface. It is supported by lead-in wires and a supporting wire which are inclined downwardly from the protected by insulating tubes, similar to those shown in Fig. 2, where they pass through the reflecting disk 22. If desired, these may be spread so as to passthr'ough the edges of the reflector disk rather than the center as shown in Fig. 5.

The polar intensity diagram of the lamp shown in Fig. 5 has been developed in the manner al ready discussed in connection with Fig. 1. Although the diagram does not show uniform intensity, and therefore indicates an asymmetrical pattern on the ceiling or wall, it will be noted that every ray striking the reflecting surfaces is reflected directly out of the bulb. 'In many cases this will be the preferable manner of, accomplishing the desired result since the ordinary bulb, preferably of a slightly larger size than normal so as to keep the filament at the proper distance from the bulb wall, can be used, without incurring the necessary expense of making special molds toproduce special shaped bulbs.

' We have thus discussed a series of characteristic features which may be embodied-in a bulb having a reflecting coating, and with the fllament either in its normal position, or lowered or offset so as to be completely hooded by the other improvement in light distribution, which is equally applicable to the bulbs shown in Figs. 3 and 4. It is obvious, in all the cases illustrated, that, except for the neck area with or without the sloping reflector, the angle between the two cut-01f or limiting rays in any plane through the fllament center, when the filament center is located on the main axis of the lamp,

is approximately 180, and is exactly 180 for a point source of light so located. When the lamp is located in a cove, with the lamp axis and the long dimension of the cove parallel, the sizeof the angle between the cut-off or limiting rays in any plane passing through the axis of the lamp is not of great importance since this determines merely the amount of overlapping from adjacent lamps. However the cut-off angle in a plane perpendicular to this lamp axis is) of importance, and should be preferably considerably less. than 180 so that the light can be thrown farther 'out onto the ceiling, for example, and with greater intensity, and so that a limited amount only will fall on the side wall 'and so none will be lost on the side of the cove. Dropping the filament below thelamp axis actually does narrow this cut-off angle, and again makespossible a more desirable light distribution, and increased efliciency of illumination.

This cut-off angle could be narrowed by silvering more than half the area of the bulb, said area being bounded by a plane, for example, parallel to, but not through, the main axis of the lampf However, this method would not be efllcient, since much of the light striking the reflecting surface would be trapped within the reflecting surfaces, and would be reflected many times beforeit was finally sent out of the bulb, and therefore with a considerably reduced intensity. The

same result might be attained by employing a bulb asymmetrical about its main axis, that is,

. it would not be a surface of revolution about the axis.

In any bulb designed for cove lighting, it is often desirable to produce a diffusing light, al-

of less importance than when used for direct lighting. A. diffusing effect can be obtained by frosting the transmitting portion of the bulb, but we prefer to accomplish this effect by employing the diffusing-reflecting surfaces, disclosed in the co-pending application of Birdseye and Deren,

Serial No. 47,581, filed October 31, 1935. By using these minutely roughened surfaces as highly efflcient reflectors we have found that the light pattern, except for the reduction of fllament images and shadows, remains approximately the same as for the non-diffusing reflecting surface of the same shape. When the light is diffused by passing through a frosted surface, or when it is diffused by being reflected from a reflecting surface having a relatively coarse rough surface-such as would be obtained by corrugating, for example-the light pattern itself becomes diffused, and accuracy of the reflecting surface, as far as directing light in certain desired directions and with predeterminedintensities in these several directions, becomes an approximation onlyr Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States, is

1. An electric lamp for cove lighting including a bulb symmetrical about the axis of the lamp having a reflecting coating applied to substantially half its surface in the area bounded by a plane in which lies the axis of the lamp, and a sloping reflector position in the neckof the bulb and making an angle of less than degrees with the axis of the lamp.

2. A reflecting electric larnp comprising a bulb,

afllament mount located symmetrically therein =whose axis is perpendicular to the axis of the bulb, a reflecting coating applied to one-half of and carrying a filament, the bulb having a reflecting coating applied to approximately half its surface and bounded by a plane in which lies 1 the axis of the mount, in combination with a reflector within the bulb neck so positioned around the mount that its longest diameter makes an angle of substantially less than 90 i with the axis of the mount, acting to reflect light out through the non-reflecting side of the bulb.

3. A reflecting electric lamp comprising a bulb having a symmetrically located filament mount and filament therein and provided with a reflecting surface bounded by a plane in which lies the axis of the mount and including approximately half the bulb area, in combination with an oval reflectorlocated within the bulbneck about the mount and adjacent the reflecting surface of the bulb and of substantially less curvature than the adjacent portion of said reflecting surface, and forming at its adjacent portions substantially a continuation of said adjacent portions of said reflecting surface.

4. A reflecting electric lamp comprising a bulb reflector having a slope substantially the same as that of the contiguousportions of said refleeting surface, and the mid-point of said neck reflector making anangle of substantially less than 90 with the axis'of the surface, whereby all the light radiated from' said filament is projected out of said bulb after undergoing not more thanonerefletion,

5. A reflecting electric lamp comprising in a single structure, a bulb, a centrally located fllawhich. with the exception of the neck portion thereof, is of the form of an ellipsoid of revolution, said neck portion being at one end thereof,

' the axis of said neck portion coinciding with the axis of revolution of said ellipse, a sloping dished neck reflector so proportioned and so placed in -said neck as substantially 'to continue the surface of said ellipsoid of revolution through the region of said neck, and substantially to flll the cross-section of said neck, and a reflecting coating applied to approximately one-half the surface of said bulb body, said coating being bounded by thelargest elliptical cross-section of said bulb. '7. A reflecting electric light buIb adapted to project all the radiation of its fllament, after not more than one reflection of any ray, into one hemisphere whose axis is perpendicular to the axis of the bulb, having a' reflecting coating apby a plane in which lies the axis of said bulb,

'- plied to one half thereof, said half being bounded and a neck reflector mounted in the bulb neck .at an angle with the axis of said bulb.

8. In an electric light bulb designed to project substantially all of its rays into a hemisphere the surface of said bulb in an area bounded by a plane in which lies the main axis of the bulb,

a fllament within the bulb, and a neck reflector mounted at such an angle with the axis of the bulb that rays from the filament to said neck reflector will be refl'ected therefrom out through the uncoated side of said bulb.

9. An electric lamp designed to project all of its rays into a hemisphere whose axis is perpendicular to the axis of the bulb and to produce a distribution of intensity in said hemisphere which is substantially symmetrical with respect to a plane perpendicular to the axis of said lamp through the line of maximum bulb diameter, comprising a bulb of form substantially ellipsoidal with the exceptionof the neck portion thereof, a reflectingcoating applied to one-half the surface of said bulb in an area bounded by a plane in which lies the major axis of said ellipsoid, a dished neck reflector mounted in the neck of said bulb in a position and at an angle with said major axis effectively to produce said ellipsoidal reflecting surface past the junction line of the body of said bulb with the neck thereof, said neck reflector and said ellipsoidal reflecting surface cooperating to project all rays f i'rom a fllament within said bulb in said designed ,manner after not more than one reflection.

10. A reflecting electric lamp-comprising a bulb symmetrical about the axis of said lamp having a reflecting coating applied to one-half thereof "and bounded by a plane in which lies the axis of said bulb, a fllament located so as to" intersect said plane, and a neck reflector mounted at an angle with the axis of said bulb.

CLARENCE BIRDSEYE. CLARENCE KJREIMAN.

CERTIFICATE OF CORRECTION. I Patent No. 2,121,511. June 21,- 1958.

CLARENCE BIRDSEYE, ET AL.

It is hereby certified that error appears in the printed specification of the above numberedpate nt requiring correction as follows Page 1;, second column, line 58, claim 9, strike out the word dished; and that the said Letters Patent should be read with this correction therein-that the same may conform to the recordiof the case in the Patent .Office.

signed and sealed this, 9th day of August, A.- D. 1958.

Les-lie Fra zer (Sea1) Acting Commissioner of Patents. 

